Semiconductors are generally manufactured by forming active devices on a semiconductor substrate and then applying one or more dielectric layers over the active devices and the semiconductor substrate. Unfortunately, the active devices are prone to failure when subjected to moisture. Ambient moisture as well as moisture from the manufacturing process readily reaches the active devices through moisture paths created through various material interfaces.
With reference to FIG. 1, an integrated heat sink down (IHSD) configuration for a semiconductor device 10 is provided to illustrate a moisture path 12 to an active device 14. As illustrated, active device 14 is formed on a surface of a substrate 16. A continuous via 18 is used to electrically couple the active device 14 to a metal panel 20, which forms a ground plane and a heat sink. The metal panel 20 and the substrate 16 are separated by one or more dielectric layers 22. The continuous via 18 is formed through the dielectric layers 22.
The continuous via 18 is made up of a sequence of alternating metal-filled vias and metal pads. A first via 24 is formed within the first dielectric layer 26, over and in contact with the active device 14. A first metal pad 28 is created over and in contact with the first via 24. Subsequently, a second via 30 is formed within the second dielectric layer 32, over and in contact with the first metal pad 28. A second metal pad 34 is created over and in contact with the second via 30. A third via 36 is formed within the third dielectric layer 38 between the second metal pad 34 and the metal panel 20. A porous epoxy 40 is used to encapsulate at least a portion of the semiconductor device 10. As illustrated, the epoxy 40 encapsulates the dielectric layers 22, the metal panel 20, and a portion of the substrate 16.
Moisture ingression through metal-dielectric and substrate-dielectric interfaces in a semiconductor device 10 may cause electrical failure over time. As illustrated in FIG. 1, moisture may reach the active device 14 through a moisture path 12 at the junction of the substrate 16 and the first dielectric layer 26. The moisture path 12 is direct and results in moisture reaching the active device 14 in a relatively short period of time. Notably, during the application of the epoxy 40, moisture is often trapped between the epoxy 40 and the dielectric layers 22. The moisture reaches the active device 14 by way of the moisture path 12. Ambient moisture readily passes through the porous epoxy 40 and reached the active device 14 through the moisture path 12.
In an effort to address such moisture issues, traditional integrated heat sink (up) configurations have employed a guard ring 42 about an active device 14 in an active device area 44 of a semiconductor device 10, as illustrated in FIG. 2. However, the guard ring 42 only delays the ingress of moisture to the active device 14 by lengthening the moisture path 12.
The guard ring 42, which is formed from a sequence of alternating metal filled via rings and metal trace rings, creates a partial barrier around the perimeter of the active device 14. Notably, the guard ring 42 does not form a hermetically sealed enclosure about the active device 14. The guard ring 42 is grounded by a ground via 46, which is formed through the substrate 16, to a backside metal panel 48. The backside metal panel 48 is a metal layer formed on the backside of the substrate 16 to assist in providing a ground for the guard ring 42. In this illustration, a first metal-filled via ring 50 is formed within the first dielectric layer 26 on an ohmic contact ring 52. A first metal trace ring 54 is created over and in contact with the first metal-filled via ring 50. Subsequently, a second metal-filled via ring 56 is formed within the second dielectric layer 32, over and in contact with the first metal trace ring 54. A second metal trace ring 58 is created over and in contact with the second metal-filled via ring 56. A third dielectric layer 38 is formed over the second dielectric layer 32 and the second metal trace ring 58.
As shown, the moisture can still reach the active device 14 by circumventing the guard ring 42. Although the moisture path 12 is extended, moisture inevitably reaches the active device 14, and failure of the active device 14 ensues.
Accordingly, there is a need to create an enclosure to significantly reduce or prevent the moisture ingression in a more efficient and effective manner. In particular, there is a need to create a metal enclosure that forms a substantially hermetic seal around the active devices on the surface of the substrate without significantly increasing the cost or complexity of the manufacturing process.